1. Field of the Invention
The invention relates to an integratable circuit configuration with an analog network.
High-accuracy networks with resistors and capacitors are still usually made by discrete or hybrid technology. Although the expenditure for circuitry is quite high, nevertheless such techniques so far have been best able to meet the necessary demand for absolute accuracy, production tolerances, long-term stability and temperature response.
In contrast, integrated circuitry networks require a very slight expenditure for circuitry. However, they have the disadvantage of producing resistors and capacitors that are subject to major fluctuations dictated by production tolerances and temperature factors. High absolute accuracy and high constancy is attainable only at considerable additional expense.
2. Description of the Related Art
However, a paper by M. Banu and Y. Tsividis, entitled "An Elliptic Continuous-Time CMOS-Filter With On-Chip Automatic Tuning", in IEEE Journal of Solid-State Circuits, Vol. SC-20, No. 6, Dec. 1985, and a paper by Y. Tsividis, M. Banu and J. Khoury, entiled "Continuous-Time MOSFET-C Filters in VLSI", in IEEE Journal of Solid-State Circuits, Vol. SC-21, No. 1, Feb. 1986, describe an integratable circuit configuration with a filter that has the usual capacitors, but its resistors are replaced by MOS field effect transistors. Triggering of the MOS field effect transistors is carried out by a phase detector connected downstream of a loop filter. The phase detector in turn compares a reference signal with the output signal of an oscillator or with the response signal of a further filter that is excited by the reference signal.
The oscillator and the further filter have MOS field effect transistors and capacitors, which are identical in layout to the MOS field effect transistors and capacitors of the first-mentioned filter. In integrated circuitry, it is assumed that instead of high absolute accuracy, a high relative accuracy between two or more components of identical layout is attained. The oscillator or the further filter is a component of a phase locked loop which, with respect to the reference signal, adjusts the oscillator or the further filter with high absolute accuracy through the MOS field effect transistors. The MOS field effect transistors of the first-mentioned filter are triggered by the same signals as the oscillator or the further filter, so that in this respect as well, high absolute accuracy is attained.
A broad field to which such analog networks applies is particularly in circuits made by switched capacitor technology, which in general are fully integratable, but in which analog filters connected upstream or downstream must usually have a discrete layout. It is therefore a goal to integrate the analog filters as well, while keeping the effort and expense therefor as low as possible. However, in the known version, the effort and expense for calibrating the analog closed-loop circuit is quite high.
It is accordingly an object of the invention to provide an integratable circuit configuration with an analog network, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type.